"Proof cannot be disclosed at this time," he said, noting that Pakistan had assured India that it will not allow use of its territory for launching attacks against this country.

Pakistan had given this assurance at a meeting Singh and Zardari had on the margins of the United Nations General Assembly session on September 24.

In an address to the nation, the Prime Minister had yesterday blamed elements outside the country for the terror strikes in Mumbai and warned that India will not tolerate the use of territory of its neighbours for attacks in the country.

India will take up "strongly with our neighbours that the use of their territory for launching attacks on us will not be tolerated, and that there would be a cost if suitable measures are not taken by them."

Singh had said the "well-planned and well-orchestrated attacks, probably with external linkages, were intended to create a sense of panic by choosing high profile targets and indiscriminately killing foreigners."